In vitro proteolysis of human plasma low density lipoproteins by an elastase released from human blood polymorphonuclear cells

Abstract

In vitro incubation of human plasma low density lipoproteins (LDL) with human blood polymorphonuclear cells (PMN) for 1 h at 37 degrees C resulted in an increased (2-4-fold) release into the medium of an enzymatic activity which co-eluted with LDL by column chromatography at physiological ionic strength but dissociated from it in high salt media in an ultracentrifugal field. The release of this enzymatic activity increased with increasing concentration of LDL in the medium and caused the hydrolysis of the LDL apoprotein B100 as indicated by the appearance of 7-8 low molecular weight bands (immunoreactive with anti-LDL) which were not present in the electropherogram of control LDL. The proteolytic activity was identified as an elastase by the following criteria: 1) capacity to hydrolyze the synthetic substrate methoxysuccinyl-Ala-Ala-Pro-Val-4-methylcoumaryl-7-amide known to be specific for the PMN elastase, 2) pattern of apo-B proteolysis identical to that exhibited by pure PMN elastase, 3) inhibition of the proteolysis by the elastase inhibitor methoxysuccinyl-Ala-Ala-Pro-Val-CH2Cl, 4) identity in molecular weight (28,000-30,000) of this activity with a pure preparation of PMN elastase labeled with [3H]diisopropylfluorophosphate. Based on thiobarbituric acid analyses and the lack of effect by vitamin E, oxidative events appeared to play no detectable role in apo-B proteolysis. Since we previously reported (Byrne, R. E., Polacek, D., Gordon, J. I., and Scanu, A. M. (1984) J. Biol. Chem. 259, 14531-14543) that high density lipoprotein-3 promotes the in vitro release of PMN elastase which cleaves apo-A-II, it is apparent that in vitro, both LDL and high density lipoprotein, two of the major plasma lipoprotein classes, can affect the export from PMN of an elastase which exhibits proteolytic action on apo-B and apo-A-II.